What is banded iron formation?
Quick Answer
Banded iron formation is a layered sedimentary rock rich in iron oxides, deposited mostly in Earth’s ancient oceans.
The Full Story
Banded iron formations, often called BIFs, are among the most important clues to early Earth’s atmosphere and oceans. They formed mainly in the Precambrian, especially between about 2.7 and 1.8 billion years ago, when iron dissolved in oxygen-poor seawater was oxidized and settled out in layers. Their alternating bands of iron-rich minerals and silica reflect changing chemical conditions in ancient marine environments. Many of today’s major iron ore deposits come from these ancient rocks.
Key Facts
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"The striped rocks that record Earth’s oxygen revolution"
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